The present invention relates to pulverized solid fuel delivery systems and, more particularly, to a nozzle assembly for use in a pulverized solid fuel delivery system.
Systems for delivering pulverized solid fuel (e.g. coal) to steam generators typically include a plurality of nozzle assemblies through which pulverized coal is delivered into a combustion chamber of the steam generator. The nozzle assemblies are typically disposed within windboxes, which may be located proximate the corners of the steam generator. Each nozzle assembly includes a nozzle tip, which protrudes into the combustion chamber. Typically, the nozzle tips are arranged to tilt up and down to adjust the location of the flame within the combustion chamber.
FIG. 1 is a partially-exploded, perspective view of a typical solid fuel nozzle assembly 200 disposed in a fuel compartment 208 of a windbox 202. As depicted in FIG. 1, the solid fuel nozzle assembly 200 comprises a nozzle tip 204 and a fuel feed pipe (conduit) 216. The nozzle tip 204 has a double shell configuration, comprising an outer shell 210 and an inner shell 212. The inner shell 212 is coaxially disposed within the outer shell 210 to provide an annular space 214 between the inner and outer shells 212, 210. The inner shell 212 connects to the fuel feed pipe 216 for feeding a stream of pulverized solid fuel entrained in air through the inner shell 212 into the combustion chamber of the steam generator. The annular space 214 is connected to a secondary air conduit 218 for feeding secondary air through the annular space 214 into the combustion chamber. The secondary air is used in combustion and helps to cool the nozzle tip 204.
The cross sectional shape of the outer shell 210 is typically rectangular and mainly corresponds to the internal cross section of an outlet end 220 of the secondary air conduit 218, which also has a rectangular cross-section. Similarly, the cross sectional shape of the inner shell 212 is typically rectangular and mainly corresponds to the external cross section of an outlet end 222 of the fuel feed pipe 216. However, the fuel feed pipe 216 typically has a round inlet end 224, which requires the use of a round-to-square or round-to-rectangular transition section between the inlet and outlet ends 224 and 222 of the fuel feed pipe 216. While this arrangement is suitable for many applications the distribution of the pulverized solid fuel as it flows through this transition section is neither uniform nor concentric. It is believed that this non-uniform solid fuel distribution can affect the performance of the nozzle 200, and may be disadvantageous in certain applications.